Heating of fluids



Oct. 31, 1944. w BARNES HEATING OF FLUIDS Filed Oct. 2:5, 1942 O 0 0 000 O O O 0 0 O 0 O 0 0-0 0 O O jQ/IZZ OIE' Patented Oct. 31, 19442,361,812

"UNITED STATES PATENT OFFICE HEATING OF FLUIDS Marion W. Barnes,Chicago, Ill., assignor to Universal Oil Products Company, Chicago,111., 'a corporation of Delaware Application October 23, 1942, SerialNo. 463,055

- high radiant heat 6 Claims. (Cl. 122-356) The invention is directed toan improved form of heater of the radiant and convection type which willbe found particularly advantageous as applied to heating hydrocarbonvapors, normally gaseous hydrocarbons or other vaporous or gaseousmaterials to high temperatures. The invention also embraces the improvedmethod of heating which may be conducted in heaters such as hereinprovided. I

Numerous industrial processes, including, for

flames and nascent hot combustion gases even when employing fuels ofrelatively low calorific example, operations conducted for effecting thea .energy from flames and hot combustion gases is practically mandatoryto obtain quick heating of heavy hydrocarbon oils, gases and vapors tohigh reaction temperatures due tothe high heat transfer rates required.However, the high heat transfer rates obtainable by radiant heating withfuels of high calorific value cannot be achieved with low grade ordiluted fuels due to their low value. Therefore, in the heater hereinprovided -I employ flue gas recirculation and also employ directradiation from the flames and nascent hot combustion gases, but limitflue gas recirculation to that section of the heater in which combustiongases which have given up a large portion of heir radiant energy aredirectly contacted with the fluid conduits through which the materialundergoing treatment is passed. In another section of the heater,through which no flue gases recycled, I provide fluid conduits disposedoutside the direct path of travel of the flames and freshly generatedhot combustion gases and transmit radiant heat directly to theseconduits from calorific value and low flameburst temperature.

Consequently, the best types of heaters commonly employed by therefining industry in thermal cracking installations, which were designedto operateon fuels of high calorific value to give *liberation andemploying a relatively high ratio of radiant heat surface to convectionsurface, are not so successful as applied to the present problems/aboveoutlined.

It is the primary object of the present invention to provide an improvedform of heater and method of eating which obviate the difficulties abovementioned, permitting the use of relatively providing high rates of heatlow grade fuels and transfer from th flames and freshly generatedcombustion gases which closely approach the maximum rates obtainablewith the particular fuel employed.

It is well known that the attainment of high heat transfer rates byconvection can be accomplished with flue gasrecirculation. However, the

rates thus obtainable are not as high as those which can be achieved bydirect radiation from said flames and hot combustion gases and fromrefractory surfaces over which the' flames and hot combustion gases arepassed before being commingled with the recycled flue gas. radiant. andconvection heating sections are maintained separate and rates of heattransmission, closely approaching the highest obtainable with theparticulartype of'fuel and type of heating employed, are obtainedln eachof these sections.

The features and advantages of the invention will be more apparent withreference to the. accompanying diagrammatic drawing which is anelevational view, shown principally in section, of

one specific form of theimproved heater provided by. the invention.

The heater illustrated in the drawing is of the general type now widelyused in the oil refining industry and known as a center-wall updraft"heater. This type of heater, Without the improvements herein provided,is described in U. S. Patent 2,147,662 toL. A. Mekler.

Referring to the drawing, theheater hereillustrated comprisessubstantially vertical refractory side walls I and 2, refractory endwalls, one of which is indicated at 3, a floor l, inwardly slopingrefractory side walls Sand '6 which connect the substantially verticalwalls I and 2, respectively. with other'vertical refractory walls 1 andv 8 between which is disposed a convection or fluid heating zone 9 ofsmaller cross-sectional area than the lower portion of the heater. 7Within the heater a pair of substantially vertical refractory walls IIIand l I, extending from beneath floor 4 to an elevation substantiallycorresponding to the base of the sloping walls 5 and 6, are disposed.Walls 10 and II are spaced from each other to provide a fluid passagewayl2 Thus, the

therebetween for recycled flue gases and are spaced from the adjacentside walls I and 2 to provide a combustion and radiant heating zone l3between walls I and I and a similar combustion and radaint heating zoneI4 between walls 2 and II. Walls l0 and H are bridged at the top by arefractory wall l5, having a plurality of openings l6 providedtherethrough at spaced points along its length through which recycledflue gases supplied to fluid passageway l2, as will be later described,are introduced into the zone I! between walls and 6.

,A bank l8 of tubular fluid conduits comprising,

in the case illustrated, a single vertical row of horizontally disposedtubes I9 is located in zone l3 adjacent wall I. Another tube bank 20,also comprising, in the case illustrated, a single substantiallyvertical row of horizontally disposed tubesZI is located in zone l4adjacent wall 2. Another tube bank 22, comprising a single row ofhorizontally disposed tubes 23, is located adjacent the sloping wall 5and another similar bank 24 of horizontally disposed tubes 25 is locatedadjacent the sloping wall 6. Another tube bank 26 comprising, in thecase illustrated, a plurality of superimposed horizontal rows ofhorizontally disposed tubes 21, is located in fluid heating zone 9.

- A row of burners, one of which is indicated at 2B, is disposed beneathzone [3 in the space 29 provided between floor 4 and sub-floor 30 and asimilar row of burners, one of which is indicated at 28', is disposedbeneath zone l4 in the space 3| provided between floor 4 and sub-floor30. Burners 28 and 28 are supplied with fuel through the respectivelines 32 and 33 in quantities regulated by the respective valves 34 and35, and air,

for combustion of the fuel is supplied to zones 29and 3| and to thecombustion zones, as will be later described. The burners project thecombustible fuel-air mixture through th firing ports 36, disposedadjacent walls l0 and II upwardly against the surfaces of the latterwithin the respective zones l3 and I4. The resulting flames and nascenthot combustion gases pass upwardly over the surfaces of walls l0 and H,heating the same to a highly radiant condition. Radiant heat istransmitted from the highly heated surface of wall l0 and fromthe flamesand hot combustion gases passing upwardly thereover directly to one sideof the tubes IS in bank l8 and the adjacent surface of wall I reradiatesheat to the opposite side of the tubes l9. In a similar manon thesetubes.

tubes of banks 3 and 20 are disposed without the main path of travel ofthe flames and hot combustion gases through zones l3 and i4 and receiveheat predominantly by radiation. In previous heaters of this generaltype, without the provisions of the present invention for recycling fluegases to zone H, the tubes of banks 22 and 24 may be excessively heated,particularly when a fuel of high calorific value is employed, due to thesuperimposing of radiant and convection heat In the heater hereinprovided, when fired with low grade fuel, a considerable portion of theradiant heat energy of the freshly generated hot combustion gases isexpended in zones l3 and I4 and, in any event, the gases leaving thesezones are commingled with recycled flue gases. Thus, the tubes of banks22 and 24 receive a much smaller component of radiant heat energy end,although the convective component is increased, are not as susceptibleto excessive heating as in previous designs of this type of heater.

The commingled combustion gases and recycled flue gases pass upwardlyfrom zone I! through zone 9 in direct and in intimate contact with the.tubes 21 of bank 26 and transmit fluid heat to ner the heated surfaceof wall H and the flames and nascent hot combustion gases passingthereover transmit radiant heat directly to one side of tubes 2i of bank20, and the opposite side of these tubes is heated by reflected radiantheat from the adjacent surface of wall 2.

The combustion gases leaving zones l3 and I4 and entering zone 1 I arecommingled with recirculated flue gases which pass from zone l2 throughopenings l6 into zone II. In passing through zone II the commingledgases transmit most of their remaining available radiant heat energy tothe tubes of banks 22 and 24 and these tubes aresalso washed bythe-commingled gases passing through zone l1, thereby receiving asubstantial component of convection heat.

When the heater is fired, as contemplated by while another regulatedquantity of the gases is directed from the zone 38, disposed above zone9, through duct 39 to a suitable hot gas fan or blower indicated at 40.The blower directs the gases through duct 4| to zone I2 between walls I0and II and therefrom through openings I6 into zone I 1, thusestablishing a flue gas cycle through zones l1 and 9 and increasing theheat supplied by convection to thetubes. of banks 22, 24 and 26 so as tomaintain relatively high heat transfer rates in these banks.

As another feature of the invention, I provide, in the case illustrated,for preheating the air employed for combustion of the fuel. This is notto be considered a limiting feature of the invention but is preferablyemployed when the heater is flred with fuel of relatively low calorificvalue,

in order to increase the flame temperature and tions separated by thepartition 45, each section comprising a plurality of relatively flatmetal plates spaced from each other to provide-relatively narrowopenings therebetween, alternate openings being open at their top andbottom to permit the passage of flue gases therethrough from zone 38 tostack 31, while the intervening openings are closed at the top andbottonf and are provided with suitable baffles 46. This type of airpreheater is well known in theyindustry and a more detailed illustrationand description is, therefore, considered unnecessary toarr/understanding of the invention.

Air is admitted to the spaces of preheater 42 which are closed at thetop and bottom through suitable air inlet ducts 41, in amountscontrolled by the dampers 48, and is preheated by direct contact andheat exchange with the gases passing through the preheater from zone 38to stack 31. The air is directed through the preheater as 7 indicated bythe dotted arrows and is directed the preheater passes downwardlythrough spaces 49 and 50, wherein it is further preheated by contactwiththe refractory walls of'the ,heater, and

enters the zones 29 and 3| through suitable ports 52 and 53 providedthrough the side walls I and 2. The preheated air passes, in part, fromzones 29 and 3| through burners 28 and 28 and, in part, directly throughfiring ports 36 into the combustion and radiant heating zones l3 and I4wherein it serves to support combustion of the fuel. Air may be drawnthrough the preheater and through the spaces "and 5|] by the inspiratingaction of the burners or, when desired, it may be supplied throughducts41 from a suitable fan or blower, not illustrated.

The present invention is not concerned with the particular flow employedfor the fluid undergoing heating in the various tube banks or theparticular sequence of the tube banks in the flow. There'are numerouspossibilities, some of which are illustrated and described in theaforementioned Mekler Patent 2,147,662, and the particular flow employedmay be selected to suit requirements. It is worthy of note, however,that the improved heater herein illustrated retains the advantages offormercenter-wall up-draft heaters in that it permits wide flexibilityof operation with respect to the flow of fluid undergoing heatingthrough the heating coil and permits the treatment of two parallelstreams of fluid under either substantially identical or differentheating conditions or the treatment of a single stream of fluid, passedin series through the various tube banks in any desired sequence, or thetreatment of two or more streams in a portion of the heating coil andtreatment of a single stream in other portions of the coil.

I claim as my invention:

- 1. A heater for fluids comprising, in combination, spacedsubstantially vertical refractory walls, other substantially verticalrefractory walls spaced from each other to define a passageway forrecirculated combustion gases therebetween, the last named walls beingdisposed between and spaced from the first named walls to defineseparatle combustion and radiant heating zones, a bank\of tubular fluidconduits disposed-adjacent one of said walls in each ofthe combustionand radiant heating zones, burners disposed adjacent one end of each ofsaid combustion and radiant heating zones to direct flames and hotcombustion each of said zones opposite said fluid conduit therein, afluid heating zon'e disposed adjacent and in communication with that endof the therefrom, a bank of tu ular fluid conduits dis-,

posedwithin said fluid h ting zone in the direct path of travel ofcombusti n gases passing there gases vertically over the surface of thatwall in through from said combustion and radiant heat ing zones, meansfor discharging combustion gases which have passed through said fluidheating zone therefrom, and means for directing regulated quantities ofthe last named gases through second named refractory walls, out ofdirect contact with the flames and hot combustion gases the aforesaidpassageway disposed between the passing through said combustion andradiant heating zones, and therefrom into direct contact with thecombustion gases passing from the latter zones to said fluid heatingzone.

2. A heater such as defined in claim 1, provided with an air preheaterdisposed within a flue leading from said fluid heating zone to a stack,and means for directing air through said preheater to said combustionand radiant heating zones to support the combustion of fuel supplied tothe latter from said burners.

3. A heater such as defined in claim' 1, provided with an air preheaterdisposed in a flue leading from said fluid heating zone to a stack, ahousing spaced from and disposed adjacent the first named refractorywalls and means for directing air through said preheater and throughmeans for passing combustion gases from the last-named zone through saidintermediate zone and said convection zone, a tube bank disposed in theradiant zone to be heated predominantly by radiation, a tube bankarranged in the intermediate zone for heating thereof by radiation andconvection, a tube bank in the convection zone disposed in the path ofthe combustion gases passing 'therethrough, means for removing thecombustion gases from the convection zone and means for introducing aregulated portion there- 1 of to said intermediate zone to commingletherein with the combustion gases from said radiant zone.

5. A fluid heating furnace comprising refrac tory vertical walls forminga radiant heating section, additional vertical walls defining aconvection heating section in vertical alignment with r and spaced fromthe radiant section, the convection section being of smallercross-sectional area than the radiant section, sloping refractory wallsjoining the first-named walls with said additional walls, and definingan intermediate'zone in the furnace, heating tubes in said radiantsection adjacent the first-named walls and means for applying radiantheat thereto, heating tubes in said intermediate zone adjacentsaidsloping walls, means for passing combustion gases from the radiant.section through said intermediate zone in heat exchange relation withthe lastmentioned tubes and then through the convection section, heatingtubes in the convection section disposed in the path of travel of thecombustion gases therethrough, means for removing the combustion gasesfrom the convection sec tion and means for introducing a regulatedportion thereof to said intermediate zone to commingle therein with-thecombustion gases from} the radiant section.

6. The furnace as defined in claim 5, further characterized in that saidmeans for a dying radiant heat comprises a refractory pargfi ti bningmember disposed in the radiant section between and spaced from thefirst-named vertical walls and burners arranged to project combustionproducts in a vertical direction along the opposite sides or saidmember.

MARION W. BARNES.

